Optimize setting uniforms

[pjcozzi]

Setting uniforms can take up to 15% of our time in the profiler, which is pretty standard in a 3D engine. We can do better, by both optimizing setting them and using less of them (yes, that means packing things together).

CC #646

[emackey]

While developing the gridMaterial, I noticed the uniforms are exposed as-is in Materials.js. Would it be worthwhile for materials to have a bit of JS interface, for example publicly exposing 4 un-related floats, while privately bundling them into a vec4 uniform? In other words, allow a material to present more public variables, and hide the bundling from the user.

[pjcozzi]

@emackey we will do something like this for materials since we don't want end users to do deal with packing directly. However, materials are not much of a problem right now compared to, say, terrain tiles and, soon, models. Generally, there are a lot more draw commands for these than for primitives supporting materials, especially when we add better batching.

[pjcozzi]

Some improvements were made in #1144

For the Everest terrain view in Sandcastle, uniform1f still shows up on the profiler. We should pack floating-point array uniforms into vec4 array uniforms. We can also better isolate uniforms that don't change between draw commands.

[pjcozzi]

It should be low-hanging fruit to replace manualUniforms with an array.

[pjcozzi]

More improvements: #2357

Plans:

• Low-ish hanging fruit: avoid lookup by uniform name when setting manual uniforms by assigning the index to each function in the uniform map in advance. This will most likely require introducing a new UniformMap.
• Pack uniforms together, including packing arrays into vectors or matrices.
• Group by static/dynamic based on semantic/user. Directly call GL for dynamic values.
  • Use this as the basis of uniform buffers - #797
  • Related: separate out uniforms for material vs. techniques

[pjcozzi]

Also see OpenGL Scene-Rendering Techniques.

[pjcozzi]

Section A.7 of the GLSL spec has some uniform packing tips.

[pjcozzi]

CC #2490 and #2493